Third generation wireless mobile user equipment will support dual radio access technology, such as by supporting communication over 3G (third generation) networks, such as wideband code division multiple access (WCDMA) networks, and 2G networks, such as Global Systems for Mobile communication (GSM) networks. Such user equipment will be required to acquire and maintain knowledge of multiple radio frequency domains with regard to signal strength of serving and adjacent cells, interference, and synchronization. When such user equipment is operating in idle mode, which is the mode in which the user equipment is not engaged in dedicated communication with a serving cell, the implementation of such procedures is straightforward.
However, where the user equipment is engaged in dedicated communication on a serving cell of one network, or domain, requiring that it both receive and transmit signals over the traffic channel, there may be a lack of time available during which measurements or synchronization of the other networks, or domains, supported by the equipment can take place. For example, if user equipment is engaged in dedicated communication with a serving cell on the Universal Terrestrial Radio Access (UTRA) domain using frequency division duplex (FDD), the user equipment must transmit during each available frame period. This effectively reduces to zero the time available for performing measuring and synchronization with a cell of a GSM network.
To overcome this problem, third generation partnership project (3 GPP) specification section 25.212 specifies “compressed mode” operation, during which the mobile user equipment, or the network, may transmit during only a portion of a frame in order to allow measurement and/or synchronization during the other portion of the frame. However, this specification requires transmissions to be performed using a smaller spreading factor, thereby necessitating a 3 dB greater transmission power to achieve a suitable bit-error rate (BER). The specified method thus severely impacts the capacity of the cell, as the number of devices operating in compressed mode will be limited by the increased power requirements.
The 3 GPP specification describes three methods for reducing the duration of transmitted signals communicated on one domain to thereby create a transmission gap enabling the mobile terminal to receive and perform measurements and/or synchronization activities on another domain. Puncturing, by which data redundancy is removed for a compressed frame to allow transmission within a shorter time period. This technique allows more data to be transmitted at the expense of error correction capability. A second technique is spreading factor reduction, by which the spreading factor is reduced by a factor of 2, thereby requiring half the time to transmit a given amount of data. However, such a reduction is at the expense of processing gain, which is applicable to both the uplink and the downlink. A third method of reducing the signal length is higher layer scheduling. These three methods are examples of compressed mode operation.
What is needed is an improved compressed mode communication.